DESCRIPTION: The proposed studies have two major goals, namely: (1) to establish an animal model of HIV perinatal transmission which can be used to test strategies to interrupt transmission; and (2) to elucidate the timing and mechanism of in utero maternal-fetal transmission. By utilizing a chronically catheterized pregnant macaque and her fetus, the maternal peripheral blood, fetal peripheral blood and amniotic fluid compartments will be simultaneously sampled over time to monitor the viral load, antibody response, and the changes in T cell populations after maternal infection with HIV-2-287. The investigators will then test two hypotheses that: (i) the maternal virologic and immunologic responses (and their time course) can predict transmission; and (ii) that the amniotic fluid exposure is a route of in utero HIV transmission.